Biodiversity and human-pathogenicity of Phialophora verrucosa and relatives in Chaetothyriales

Abstract

Phialophora as defined by its type species P. verrucosa is a genus of Chaetothyriales, and a member of the group known as 'black yeasts and relatives'. Phialophora verrucosa has been reported from mutilating human infections such as chromoblastomycosis, disseminated phaeohyphomycosis and mycetoma, while morphologically similar fungi are rather commonly isolated from the environment. Phenotypes are insufficient for correct species identification, and molecular data have revealed significant genetic variation within the complex of species currently identified as P. verrucosa or P. americana. Multilocus analysis of 118 strains revealed the existence of five reproductively isolated species apparently having different infectious potentials. Strains of the sexual morph Capronia semiimmersa cluster within P. americana. The newly defined taxa differ markedly in their predilection for the human host.

Keywords: Chaetothyriales; Phialophora; chromoblastomycosis; phaeohyphomycosis; phylogeny; taxonomy.

Fig. 1

Colony diameters at various temperatures ranging from 21–40 °C, measured after 3 wk on 2 % MEA.

Fig. 2

Neighbour-Joining tree obtained from the 141 ITS sequences data. Bootstrap values above 80 % are shown at the nodes. The carrionii-clade is selected as outgroup. P, E, A, U after strain number mean sources: patient, environment, animal and unknown.

Fig. 3

Maximum-Parsimony (MP) tree obtained from the combined DNA sequence data from three loci (ITS, BT2 and TEF1). Bootstrap values of Neighbour-Joining (NJ), Maximum-Likelihood (ML) and MP above 80 % / Bayesian (BS) posterior probability value above 0.80, are shown at the nodes (NJ/ML/MP/BS). Type strains and supported branches are drawn in bold. The carrionii-clade is selected as outgroup. Sources of isolation are mentioned at each strain.

Fig. 4

Phialophora verrucosa (CBS 140325). a. Colonies grown on MEA for 3 wk; b. colonies grown on OA for 3 wk; c–k. micromorphology showing phialides and conidia. — Scale bar = 10 μm.

Fig. 5

Phialophora chinensis (CBS 140326). a. Colonies grown on MEA for 3 wk; b. colonies grown on OA for 3 wk; c–h. micromorphology showing phialides, conidia, torulose hypha and muriform-like cells. — Scale bar = 10 μm.

Fig. 6

Phialophora americana (CBS 281.35). a. Colonies grown on MEA for 3 wk; b. colonies grown on OA for 3 wk; c–j. micromorphology showing phialides, conidia and torulose hypha. — Scale bar = 10 μm.

Fig. 7

Phialophora tarda (CBS 111589). a. Colonies grown on MEA for 3 wk; b. colonies grown on OA for 3 wk; c–k. micromorphology showing phialides and conidia. — Scale bar = 10 μm.

Fig. 8

Phialophora expanda (CBS 140298). a. Colonies grown on MEA for 3 wk; b. colonies grown on OA for 3 wk; c–l. micromorphology showing phialides, conidia and torulose hypha. — Scale bar = 10 μm.

Fig. 9

Phialophora ellipsoidea (CBS 286.47). a. Colonies grown on MEA for 3 wk; b. colonies grown on OA for 3 wk; c–k. micromorphology showing phialides and conidia. — Scale bar = 10 μm.

Fig. 10

Phialophora macrospora (CBS 273.37). a. Colonies grown on MEA for 3 wk; b. colonies grown on OA for 3 wk; c–k. micromorphology showing phialides and conidia. — Scale bar = 10 μm.